The International Standard Classification is the most commonly used classification of halitosis and was first proposed by Tsutomu Yae and Hideo Miyazaki. Through the observation and analysis of a large number of cases of halitosis, they first proposed the idea that “the classification of halitosis should follow the basic principles of halitosis treatment needs”. The idea received wide attention and lively discussion, and the international standard classification of halitosis was formally established at the third meeting of the Vancouver International Halitosis Forum on March 13, 1999, after the demonstration of Columbia University and the University of California. The standard will be divided into three categories of halitosis: true halitosis p pseudohalitosis and halitosis phobia. 1, true halitosis: including patients with complaints of halitosis symptoms, self-consciousness of oral odor outside, others have the same feeling or halitosis to a degree that is intolerable to those around; measured with a sulfide detector to prove that the breath contains high hydrogen sulfide. True halitosis is divided into physiological halitosis and pathological halitosis. Physiological halitosis is the cause of bad breath mainly from the tongue, after a period of tongue cleaning and attention to oral hygiene, bad breath symptoms will be significantly improved; pathological halitosis is mainly caused by oral pathology or systemic diseases. Among them, pathological halitosis caused by oral pathology is called orogenic halitosis such as: gingivitis, periodontitis, mucosal ulcerative stomatitis, post-extraction trauma healing period and malignant tumor; halitosis caused by systemic diseases is called non-orogenic halitosis such as: fruity halitosis in patients with diabetes, ammonia halitosis in patients with liver disease and urinary halitosis in patients with kidney disease. Research has found that 90% of the clinical pathological halitosis belongs to the orogenic halitosis. 2, pseudo-bad breath: is a self-conscious oral odor but others can not prove the existence of bad breath; with sulfide detector test, hydrogen sulfide gas concentration is within the normal range of patients. Such patients are mostly caused by psychological factors, and their complaints of bad breath does not actually exist. 3, halitosis phobia: refers to both patients with true halitosis and patients with pseudo halitosis, through the relevant clinical treatment, clinical symptoms have disappeared, but the patient’s psychological barriers have not been eliminated, but still want to continue to treat the situation. The significance of the international standard classification is that in clinical treatment, the physician can take a history and relevant tests, categorize according to the international standard classification, and then follow the principle of therapeutic needs, start the corresponding prevention and treatment.